Field of the Invention
The invention relates generally to a forged lift anchor for precast concrete shapes. In one aspect, the invention relates to a forged lift anchor configured for coupling with shear bars that are selectively positionable to accommodate various conditions of shear loading.
Description of the Related Art
It is known to utilize precast Portland cement concrete shapes, such as panels and tees, at a construction project. Because these building elements may be very heavy, cranes, helicopters, and other heavy equipment may be used for handling and transportation.
Metal lift anchors may be integrated into building elements during precasting of the concrete. The lift anchors may be partly embedded in the shapes, and partly exposed for coupling with hooks, cables, chains, and other lifting and moving devices after the concrete has cured.
Handling and transportation of heavy concrete shapes invariably includes lifting the shapes utilizing embedded lift anchors. This may subject the lift anchors to high tensile loads that are, in turn, imposed on the concrete. Furthermore, Portland cement concrete generally has a low strength in tension, typically 10% to 15% of its compressive strength. Therefore, lifting operations may result in 1) failure of the anchor in tension, 2) pull-out of the anchor from the concrete, 3) failure of the concrete, or 4) a combination of one or more of these failure modes.
Referring to FIG. 1, a failure of Portland cement concrete in tension is illustrated, involving a large force 32 applied to a lift anchor 24. The force 32 may remove a portion of the concrete mass 12, with the lift anchor 24 remaining in the concrete. The illustrated known failure mode 10 may be characterized by a “shear cone” 14. Referring also to FIG. 2, the shear cone 14 may be defined for purposes of lift anchor evaluation as a right circular cone having a 45° shear angle α extending from the surface 16, 22 of the concrete 12 to a vertex 30 corresponding generally with the bottom of the lift anchor 24. The shear cone failure surface 28 may be characterized as an inclined surface centered about the lift anchor 24, 40, and reflected in a conically-shaped shear cavity 18.
Oblique loading 44 of an embedded lift anchor 24, 40, such as during tilting of a precast concrete panel from a horizontal position to a vertical position, may result in a tensile component 46 and a shear component 48 acting on the lift anchor 24, 40. These load components 46, 48 may vary in magnitude during a handling process. Thus, a lift anchor should have sufficient strength to accommodate anticipated loading configurations, yet be cost-effective and have suitable dimensions and weight to readily enable placement of the lift anchor and integration with other concrete reinforcing members. Additionally, a desire to handle heavier concrete shapes may dictate the use of larger, heavier, and/or a greater number of known lift anchors. This, too, may be inconsistent with optimal cost-effectiveness, and placement and integration of known lift anchors.
A need may therefore exist for a cost-effective lift anchor for precast concrete building shapes that exhibits a suitable strength and a compact configuration.